Method for IPv4 application transition over IPv6 networks

ABSTRACT

A network system adopting a first IP protocol is provided. The network system includes an address allocating server and a communication terminal supporting both the first IP protocol and a second IP protocol, wherein the address allocating server dynamically allocates an address of the second IP protocol to the communication terminal. The communication terminal includes a dynamic address manager for acquiring the dynamically allocated address of the second IP protocol of the communication terminal from the address allocating server and a second IP protocol address of the destination of a second IP protocol packet from a second IP protocol application, and an address adapter for encapsulating the second IP protocol packet from the second IP protocol application into a first IP protocol packet, wherein the second IP protocol address of the communication terminal in the header of the second IP protocol packet and the second IP protocol address of the destination are encapsulated into the first IP protocol packet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under 35 U.S.C. 371(c) claiming priority ofPCT Application No. PCT/EP2006/062268 filed May 12, 2006 and ChinesePatent Application No. 200510072984.5 filed May 25, 2005, the entiretext of which are specifically incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a network system, a method of managingthe network system, a communication terminal and a method for sendingpackets.

BACKGROUND OF THE INVENTION

With the increasing expansion of the Internet, the existing IPv4addresses composed of 32 bits are scarce. Accordingly, an IPv6 protocolemploying an IP address of 128 bits has been proposed to thoroughlysolve the problem of scarcity of the IPv4 addresses. IPv6 protocol hassignificant improvements on addresses capacity, security, networkmanagement, mobility and quality of service, etc. Before IPv6 protocolbecomes the mainstream protocol, IPv4 protocol is continuously used,thus the coexistence of IPv4 network and IPv6 network occurs. Inaddition, due to imbalance of address allocation, some countries orregions still have enough IPv4 address space for allocation, thus IPv4network will exist in these countries and regions for a long time. In apredictable future, IPv4 network and IPv6 network will coexist for along time.

A situation exists today, which is an IPv4 application can not run in anIPv6 environment, and an IPv6 application can not run in an IPv4environment. In addition, during transition from IPv4 to IPv6, sincemost of the existing applications are based on IPv4 protocol and IPv6applications and services are relatively fewer than mature IPv4applications and services, the IPv6 network resources are inevitablywasted.

In view of the above situation, the solution of enabling the existingIPv4 applications to run over the IPv6 network inevitably requires to beimplemented. That is to say, it is desired to not only deploy new IPv6networks, but also continue to use existing IPv4 application resources.

There are several solutions proposed in the prior art for the aboveproblem. One is Dual Stack Transition Mechanism (DSTM). The object ofDSTM is to solve the problem of connecting the dual stack hosts in thepure IPv6 network to the existing IPv4 hosts or applications. The gistof DSTM is to provide a measure for obtaining a temporal IPv4 addressfor an IPv6 node, and simultaneously add a gateway between the networksof different network protocols to achieve transmitting IPv4 traffic overthe pure IPv6 network by using an IPv4 over IPv6 tunnel. This solutionregards the IPv6 network as an IPv4 intranet, and thus is effective onlyin the intranet, and can not support an IPv4 address embeddedapplication.

Another is an address translation mechanism, for example, NetworkAddress Translator-Protocol Translator (NAT-PT); Bump in the Stack (BIS)and Bump in the API (BIA), etc. Under the address translation mechanism,the address of the IPv4 packet is translated into the IPv6 address andthen transmitted in the IPv6 network, and vice versa. However, thistranslation mechanism inevitably results in large additional effort. Inparticular, when the IPv4 packet is embedded with an IPv4 address, anapplication gateway/proxy, etc, is required to translate the addressembedded in the packet, which requires more translation amount andoccupies more system resources. For example, for BIA, since it isrequired to transform the IP address (for example, FTP) embedded in theapplication layer protocol, such mechanism may be inapplicable to thosenew applications with addresses contained in their load.

A further solution is to modify the code for upgrading the IPv4application to make the IPv4 application to be an IPv6 application,which requires re-coding and testing, and consumes time and efforts.

In the prior art, a DTTS technique has been proposed to solve theproblem of running the IPv4 application over the IPv6 network. DTTStechnique does not require NAT or application gateway/proxy, etc.However, DTTS occupies limited IPv4 address resources for allocatingdynamic addresses when transforming the addresses, and transforms theIPv4 address into the IPv6 address by using an IPv4 compatible addresswhen transforming the addresses, thus the transmitting apparatus needs128-bit static routing configuration, which results in a heavy cost.

SUMMARY OF THE INVENTION

To ameliorate the problems mentioned above in the prior art, an objectof the invention is to provide seamless transition of applicationsbetween different protocols.

The present invention thus provides, in a first aspect, a network systemadopting a first IP protocol, the network system comprising an addressallocating server and a communication terminal supporting both the firstIP protocol and a second IP protocol different from the first IPprotocol, wherein the address allocating server dynamically allocatingan address of the second IP protocol to the communication terminal,characterized in that: said communication terminal comprises: a dynamicaddress manager for acquiring said dynamically allocated address of thesecond IP protocol of said communication terminal from the addressallocating server and a second IP protocol address of the destination ofa second IP protocol packet from a second IP protocol application, andan address adapter for encapsulating the second IP protocol packet fromthe second IP protocol application into a first IP protocol packet,wherein the second IP protocol address of said communication terminal inthe header of the second IP protocol packet and the second IP protocoladdress of the destination are encapsulated into said first IP protocolpacket, and said communication terminal sends out said encapsulatedfirst IP protocol packet.

A second aspect of the present invention provides a management method ofa network system adopting a first IP protocol, the network systemcomprising a communication terminal supporting both the first IPprotocol and a second IP protocol different from the first IP protocol,characterized in that: in said communication terminal, acquiring adynamically allocated address of the second IP protocol of saidcommunication terminal from an address allocating server and a second IPprotocol address of the destination of a second IP protocol packet froma second IP protocol application; in said communication terminal,encapsulating the second IP protocol packet from the second IP protocolapplication into a first IP protocol packet, wherein the second IPprotocol address of said communication terminal in the header of thesecond IP protocol packet and the second IP protocol address of thedestination are encapsulated into said first IP protocol packet, and insaid communication terminal, sending out said encapsulated first IPprotocol packet.

A third aspect of the present invention provides a communicationterminal supporting both a first IP protocol and a second IP protocoldifferent from the first IP protocol, the communication terminalconnected to an address allocating server for dynamically allocating anaddress of the second IP protocol thereto, characterized in that: saidcommunication terminal comprises: a dynamic address manager foracquiring said dynamically allocated address of the second IP protocolof said communication terminal from the address allocating server and asecond IP protocol address of the destination of a second IP protocolpacket from a second IP protocol application, and an address adapter forencapsulating the second IP protocol packet from the second IP protocolapplication into a first IP protocol packet, wherein the second IPprotocol address of said communication terminal in the header of thesecond IP protocol packet and the second IP protocol address of thedestination are encapsulated into said first IP protocol packet, andsaid communication terminal sends out said encapsulated first IPprotocol packet.

A fourth aspect of the present invention provides a method of sendingpacket for a communication terminal supporting both a first IP protocoland a second IP protocol different from the first IP protocol, thecommunication terminal connected to an address allocating server fordynamically allocating an address of the second IP protocol thereto,characterized in that, the method comprising: acquiring a dynamicallyallocated address of the second IP protocol of said communicationterminal from the address allocating server and a second IP protocoladdress of the destination of a second IP protocol packet from a secondIP protocol application, and in said communication terminal,encapsulating the second IP protocol packet from the second IP protocolapplication into a first IP protocol packet, wherein the second IPprotocol address of said communication terminal in the header of thesecond IP protocol packet and the second IP protocol address of thedestination are encapsulated into said first IP protocol packet, andsaid communication terminal sends out said encapsulated first IPprotocol packet.

According to the invention, the second IP protocol application isenabled to run seamlessly between the dual-stack hosts of the first IPprotocol network.

According to the invention, since the upper layer application requiresno modification, the invention is transparent to the upper layerapplication and will not exert an additional load to the upper layerusers.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the invention will be more apparent by thedetained description of the preferred embodiments of the invention, withreference to the accompanying drawings, in which

FIG. 1 is a schematic diagram showing an embodiment of the invention.

FIG. 2 is a block diagram showing the function of the host according toan embodiment of the invention.

FIG. 3 shows the structure of an address-mapping table according to anembodiment of the invention.

FIGS. 4A and 4B are flowchart diagrams showing obtaining the IPv4address of the destination host according to an embodiment of theinvention.

FIG. 5 is a flowchart diagram showing a process of encapsulating theIPv4 packet from an IPv4 application into the IPv6 packet according toan embodiment of the invention.

FIGS. 6A and 6B are schematic diagram showing the packet format ofencapsulating the IPv4 packet into the IPv6 packet according to anembodiment of the invention.

FIG. 7 is a block diagram showing the function of the destination host.

FIG. 8 is a flowchart diagram showing a process of the destination host.

FIG. 9 is a flowchart diagram showing a process of releasing addressaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

For the sake of illustration, the invention is based on the followingnetwork environment, that is, the host for communication is a dual-stackhost, which operates in a pure IPv6 network and runs existing IPv4applications. However, the invention is not restricted to IPv4 protocoland IPv6 protocol, and can be applied to any network employing an IPprotocol.

An embodiment of the invention will be described now with reference toFIG. 1.

In FIG. 1, a dual-stack host 101 and a dual-stack host 115 aredual-stack hosts that support both IPv4 protocol and IPv6 protocol in anIPv6 network. For those skilled in the art, the invention can be appliedto any communication terminal that support IPv4 protocol stack and IPv6protocol stack. For the sake of illustration, the terminal is referredto as the host hereinafter. The hosts 101 and 115 have respective IPv6addresses. The hosts 101 and 115 communicate with each other through anIPv6 network 110.

The hosts 101 and 115 run not only IPv4 applications but also IPv6applications. According to an embodiment of the invention, when both thehosts 101 and 115 run the IPv4 applications and the IPv4 applicationscommunicate with each other through the IPv6 network, the IPv4applications can be run seamlessly over the IPv6 network. The aboveprocedure will be described in detail later.

A DNS server 120, in response to a request for acquiring the IPv6address of the local or destination host from the host 101 or 115,analyzes and acquires IPv6 address of the local or destination host, andreturns it to the host 101 or 115, or simultaneously sends the IPv6address of the local or destination host to an address allocating server105 to allocate a corresponding IPv4 address.

The address-allocating server 105, in response to a request forallocating a temporal IPv4 address from the host 101 or 115, dynamicallyallocates the IPv4 address, and reclaims the allocated IPv4 address forfuture usage, according to actual situations.

It would be appreciated for those skilled in the art that, the DNSserver 120 and the address allocating server 105 may be combinedtogether to achieve the combined function.

FIG. 2 is a block diagram showing the function of a source hostaccording to an embodiment of the invention. The host includes at leastan address adapter 205 and a dynamic address manager 225.

The address adapter 205 encapsulates an IPv4 packet from an IPv4application 201 into an IPv6 packet, and vice versa, and maintains thecorrespondence between the IPv4 and IPv6 addresses of the host. Theoperation of the address adapter 205 will be described in detail later.

The dynamic address manager 225 acquires the IPv4 address of the localor destination host dynamically (temporally) from the address allocatingserver 105, and releases the acquired IPv4 address in order todynamically manage the IPv4 address. The function of the dynamic addressmanager 225 will be described in detail later.

The address adapter 205 includes an address-mapping table manager 210, apacket translator 215 and an address-mapping table 220.

The address-mapping table manager 210 manages the address-mapping table220. The packet translator 215 encapsulates the IPv4 packet from theIPv4 application 201 into the IPv6 packet, and vice versa, withreference to the address-mapping table 220. The address-mapping table220 may be stored in a storage not shown in FIG. 1.

The above functional blocks may be combined or separated to achieve thecombined or separated function. For example, the address-mapping tablemanager 210 and the dynamic address manager 225 may be combined into afunctional block to achieve the dynamic management of the addresses inthe address-mapping table. In addition, the address adapter 205 and thedynamic address manager 225 are preferably located between the IP layerand the Link and Physical layer to achieve the transformation of IPaddresses.

The IPv4 application 201 may be any IPv4 application in the applicationlayer.

FIG. 3 shows the structure of the address-mapping table 220.

The address-mapping table 220 correspondingly stores the IPv4 addressand the IPv6 address of hosts in the network. According to theinvention, the address-mapping table 220 maintains not only theIPv4/IPv6 address pair of the local host, but also the IPv4/IPv6 addresspair of the destination host used by the IPv4 application.

The process of acquiring the IPv4 address of the local host ordestination host dynamically (temporally) and storing it according tothe invention is described below.

FIG. 4A shows the process of dynamically acquiring the IPv4 address ofthe local host and storing it according to the invention.

First, in step S401, when the address-mapping table 220 is initialized,for example, each time the host logs on the IPv6 network or the firstIPv4 application of the local host starts to run, an IPv6 addressmanager not shown in the invention acquires the IPv6 address of thelocal host from the DNS server 120 through a transceiver 230.

In step S405, the dynamic address manager 225 sends a request containingthe IPv6 address of the local host acquired by the IPv6 address managerto the address allocating server 105.

The address-allocating server 105 dynamically allocates an IPv4 addressto the host in response to the received request, and transmits theIPv4/IPv6 address pair of the host to the transceiver 230.

In step S410, the dynamic address manager 225 acquires the IPv4/IPv6address pair of the local host from the transceiver 230.

Then in step S415, the dynamic address manager 225 informs theaddress-mapping table manager 210 that the IPv4/IPv6 address pair of thelocal host will be correspondingly stored.

In step S420, in response to the notification, the address-mapping tablemanger 210 correspondingly stores the IPv4/IPv6 address pair of thelocal host into the address-mapping table 220.

Through the above processes, the local host will temporally acquire anIPv4 address when the address-mapping table is initialized. Thereafter,all the IPv4 applications coexisted in the local host will use the sameIPv4 address. Therefore, according to the invention, the IPv4 addressspace will be used farthest.

It will be appreciated by those skilled in the art that, the aboveprocesses may be appropriately modified. For example, the local host maydirectly send the request for acquiring the IPv4/IPv6 address pair tothe DNS server 120 which acquires a dynamically allocated IPv4 addressfrom the address allocating server 105 and then returns the IPv4/IPv6address pair to the local host.

In addition, although in the above depiction, the local host acquiresthe IPv4/IPv6 address pair from the address allocating server, thoseskilled in the art would appreciate that, the address allocating servermay only return the IPv4 address.

FIG. 4B shows a flowchart for obtaining the IPv4 address of thedestination host according to the invention.

First, in step S450, the IPv4 application 201 of the local host sendsthrough the transceiver 230 to the DNS server 120 a request foracquiring the IPv6 address of the destination host.

In response to the request, the DNS server 120 returns the IPv6 addressof the destination host to the local host.

In step S455, the dynamic address manager 225 sends the requestcontaining the IPv6 address of the destination host to the addressallocating server 105 through the transceiver 230, in order to requestacquiring the IPv4/IPv6 address pair of the destination host.

The address-allocating server 105, in response to the received request,allocates an IPv4 address to the destination host dynamically, and sendsthe IPv4/IPv6 address pair of the destination host to the transceiver230.

In step S460, the dynamic address manager 225 acquires the IPv4/IPv6address pair of the destination host from the transceiver 230.

Then in step S465, the dynamic address manager 225 informs theaddress-mapping table manager 210 to correspondingly store the IPv4/IPv6address pair of the destination host.

In step S470, in response to the notification, the address-mapping tablemanager 210 correspondingly stores the IPv4/IPv6 address pair of thedestination host into the address-mapping table 220.

Through the above processes, the IPv4 address of the destination hostwill be temporally obtained when running the IPv4 application.

Therefore, when generating the IPv4 packet for the IPv4 application, theheader of the IPv4 packet may be formed by directly referring to theIPv4 address in the address-mapping table 220. Since the process forforming the IPv4 header may be achieved by using existing techniques,the description thereof is thus omitted. It is assumed in the inventionthat, the header of the packet from the IPv4 application includes theIPv4 address of the source and destination.

For those skilled in the art, the IPv4/IPv6 address pair of thedestination host may be obtained by other known means, for example, theIPv4/IPv6 address pair of the counterpart may be obtained by a directcommunication with the destination host.

FIGS. 6A and 6B are diagrams showing the format of the packet accordingto the invention, when the IPv4 packet is encapsulated into the IPv6packet.

FIG. 6A shows the format of the IPv4 packet according to the invention,including an IPv4 header 601 and an IPv4 payload 605.

FIG. 6B shows the format of the IPv6 packet according to the invention,when the IPv4 packet is encapsulated into the IPv6 packet.

The IPv6 header 601′ is a conventional IPv6 header under IPv6 protocol,which includes the IPv6 addresses of the source and destination hostscorresponding to the IPv4 addresses of the source and destination hostscontained in the IPv4 header.

The IPv4 payload 605′ and the IPv4 payload 605 have the same content.

An extension header 602′, compared with the IPv4 header 602, furtherreserves the information of the original IPv4 header of the IPv4 packetfrom the IPv4 application, i.e., the IPv4 header information containingthe IPv4 address of the source and destination hosts. In thisembodiment, the original IPv4 header is totally placed in the extensionheader. However, more preferably, the IPv4 header is compressed, but atleast the IPv4 address information of the source and destination hostsis placed in the extension header, in order to reduce informationoccupancy. In addition, a flag is optionally arranged in the extensionheader 602′ to identify whether the IPv6 packet has encapsulated theIPv4 header. In this manner, the original IPv4 header information willbe extracted by using the IPv6 packet format in the invention, when theIPv6 extension header is processed in the IPv6 protocol stack at thedestination host. And the original IPv4 packet will be restored by usingthe extracted original IPv4 header information together with the IPv4overhead, without resulting in processing the IPv4 packet by an IPv6application.

In the invention, although the original IPv4 header information isincluded as the content of the extension header in the IPv6 packet andoccupies the information resource, the inventor has discovered viaresearch that, the extension header in the IPv6 packet may absolutelyinclude optional information that needs to be processed by a destinationnode, without increasing the system overhead.

A preferable method is that, when encapsulating, for example, whenencapsulating the IPv4 packet into the IPv6 packet, idle fields in theIPv4 packet may be deleted to save the space occupied by theinformation.

While encapsulating the IPv6 packet into the IPv4 packet, idle fields inthe IPv6 packet may be deleted to save the space occupied by theinformation.

FIG. 5 shows a process of transforming the IPv4 packet from the IPv4application 201 into the IPv6 packet according to the invention.

First, in step S501, the packet translator 215 receives the IPv4 packetfrom the IPv4 application 201. In step S510, the packet translator 215looks up the address-mapping table 220 to search for the IPv6 addresscorresponding to the destination host. Then the process advances to thestep S515 where the IPv4 packet is encapsulated into the IPv6 packetaccording to the format as shown in FIG. 6B, wherein the original IPv4header is encapsulated into the extension header 602′.

Then in step S520, the transceiver 230 sends out the encapsulated IPv6packet through the IPv6 network 110.

FIG. 7 is a block diagram showing the function of the destination host.

The structure of the destination host is the same as that of the sourcehost as shown in FIG. 2, including at least an address adapter 705 and adynamic address manager 725. The address adapter 705 decapsulates theIPv6 packet and transforms it into the original IPv4 packet.

The dynamic address manager 225 may acquire the IPv4 address of thelocal host from the address allocating server 105 dynamically(temporally) according to the operation of FIG. 4A, and may acquire theIPv4 address of the local host from the encapsulated IPv6 packetreceived from the counterpart.

The address adapter 205 includes the address-mapping table manager 210,the packet translator 215 and the address-mapping table 220. Thefunction of the above functional blocks will be described in detaillater.

Those skilled in the art would appreciate that the above functionalblocks may be combined or separated to achieve the combined or separatedfunction. For example, the address-mapping table manager 710 and thedynamic address manager 725 may be combined into a function block toachieve the dynamic management of the addresses in the address-mappingtable. In addition, the address adapter 705 and the dynamic addressmanager 725 are located between the IP layer and the Link and Physicallayer to achieve the transformation of IP addresses.

FIG. 8 shows a process after the destination host receives the IPv6packet.

In step S801, when the transceiver 730 of the destination host receivesthe IPv6 packet, it forwards the IPv6 packet to the packet translator715 of the destination host.

In step S805, the packet translator 715 judges whether the IPv6 packethas encapsulated the IPv4 packet, for example, by detecting the flagarranged in the extension header 602′. If it is judged that the IPv6packet has not encapsulated the IPv4 packet, the IPv6 packet isdelivered to the IP layer for normal IPv6 packet process.

If the IPv6 packet has encapsulated the IPv4 packet, the processadvances to step S810.

In step S810, the packet translator 715 extracts the IPv6 address of thesource host from the IPv6 packet encapsulating the IPv4 packet, andforwards the same to the address-mapping table manager 710.

In step S815, the address-mapping table manager 710 compares the IPv4address of the source host in the extension header 602′ with the recordin the address-mapping table 220, with the extracted source IPv6 addressas an index.

When there is no IP address record corresponding to the source host orthe recorded IPv4 address of the source host is not in consistent withthe source IPv4 address extracted from the IPv6 packet, the processadvances to the step S820, where the address-mapping table manager 710modifies the corresponding record in the address-mapping table 220 tothe IPv4/IPv6 address pair in the IPv6 packet. Then the process advancesto step S825. The modification operation made by the address-mappingtable when the recorded IPv4 address of the source host is inconsistentwith the source IPv4 address extracted from the IPv6 packet,substantively and simultaneously performs the release operation of thecorresponding IPv4/IPv6 address pair of the source host from thedestination host.

When the recorded IPv4 address of the source host is consistent with thesource IPv4 address extracted from the IPv6 packet, the process advancesto step S825 where the packet translator 715 transforms the encapsulatedIPv6 packet into the IPv4 packet.

In this way, the IPv4 application 701 of the destination host may usethe transformed IPv4 packet as its original form and continue to run asusual.

The process of transmitting data from the application 701 of thedestination host to the application 201 of the source host is the sameas the process of transmitting data from the application 201 of thesource host, the description thereof is thus omitted.

It can be seen from the above depiction that, by encapsulating theoriginal IPv4 packet into the IPv6 packet, the invention enables thedestination host to decapsulate the IPv4 packet from the IPv6 packet foruse in the IPv4 application, without modifying the IPv4 application. Inparticular, when the IPv4 packet is embedded with the IPv4 address, theadvantage of the invention is particularly prominent. Therefore, theinvention improves the flexibility of running the IPv4 application overthe IPv6 network in a simple way.

In addition, the invention achieves the normally running of the IPv4application over the IPv6 network only by encapsulating anddecapsulating the IPv6 packet at the host side without adding additionalelements for transforming addresses such as application gateway orproxy, the invention enables the IPv4 application to run normally overthe IPv6 network with a lower cost and in a convenient form.

According to the invention, the dynamic address manager at the host sideeffectively uses the IPv4 address space, to enable the IPv4 applicationto continue to run over the pure IPv6 network.

In addition, although the foregoing is described by taking example forthe dual-stack host in the IPv6 network, those skilled in the art wouldappreciate that, the invention may be further extended to make IPv4applications (for example, in the local host) communicate with IPv6applications (for example, in the remote host) in the pure IPv6 network,as BIS/BIA does; or make IPv4 applications communicate with each otherbetween the IPv6 network and the IPv4 Internet, as DSTM does. The aboveimplementations only require adding a gateway to support anIPv4-over-IPv6 tunnel.

The process of releasing the IPv4 address according to the inventionwill be described below.

FIGS. 4A and 4B introduce the process of acquiring the IPv4 address ofthe source host and the destination host from the address allocatingserver 105, which is achieved by the address allocating server 105 byusing existing dynamic address allocating techniques, such that aplurality of hosts may share limited IPv4 address resource.

The dynamic address manager of the invention further manages thedynamically allocated IPv4 address, and releases the allocated IPv4address when necessary.

The process of releasing addresses according to the invention will bedescribed below with reference to FIGS. 9 and 2.

First, in step S901, the dynamic address manager 225 receivesinformation of ending of the application from the IPv4 application 201.

Here, the so called ending of IPv4 application may be judged accordingto a definition to the ending of the application by a particularprotocol or by an obvious ending frame.

In step S905, the dynamic address manager 225 deletes (or marks) theIPv4/IPv6 address pair of the destination host related to the ended IPv4application in the address-mapping table 220, and if it is necessary, itmay also delete the IPv4/IPv6 address pair of the local host.

In step S910, the dynamic address manager 225 informs the addressallocating server 105 the release of the IPv4 address of the destinationhost (and/or local host).

In step S915, in response to the information, the address allocatingserver 105 marks the IPv4 address allocated to the destination host(and/or local host) as available, in order to reallocate the IPv4address to other destination hosts.

In addition, in place of steps S910 and S915, the address allocatingserver 105 may voluntarily delete the IPv4 address dynamically allocatedto the host at its side, when it fails to receive the IPv4 address ofthe released host from the host for a time period.

Through the above release process, the invention can fully utilizelimited IPv4 resource. In particular, even if the host does not poweroff, the invention can release the IPv4 address timely. It is to benoticed that, the embodiments described above merely intend toillustrate the invention, and do not limit the invention.

The object of the invention can be reached by providing to the system orapparatus directly or indirectly a storage medium storing program codeof software for implementing the function of the embodiments, readingout the program code and performing the same by a computer of the systemor apparatus. At this time, so long as the system or apparatus has thefunction of the program, the implementation is not limited to theprogram.

Therefore, the program code installed in the computer can achieve theinvention since a computer can achieve the function of the invention. Inother words, the claims of the invention also comprise the computerprogram for realizing the function of the invention.

Then, so long as the system or apparatus has the function of theprogram, the program can be executed by any means such as object code,the program executed by the interpreter or the script data provided tothe operation system.

The storage medium for providing the program code comprises for example,floppy disk, hard disk, optical disk, magneto-optic disk, CD-ROM, CD-R,CD-RW, magnetic tape, non-volatile storage card, ROM and DVD (DVD-ROMand DVD-R), etc.

For the way of providing the program, a client computer may be connectedto a website in the Internet via a browser in the client computer. Thecomputer program of the invention or a compressed file automaticallysetup by the program may be downloaded to the recording medium such ashard disk. Further, the program according to the invention may beprovided by segmenting the program code constituting the program into aplurality of files and downloading the same from different websites. Inaddition, the claims of the invention also comprise a solution that aWWW server downloads a program file for achieving the function of theinvention to a plurality of users.

Moreover, the program according to the invention may be encrypted andstored into the storage medium such as CD-ROM to be distributed tousers, which allows the users satisfying certain requirements todownload encrypted encryption information via the Internet, and allowsthe users to decrypt the encrypted program by using the encryptioninformation, such that the program is installed into the computers ofthe users.

Besides the computer executable program achieving the functions of theembodiments of the invention, the operation system running on thecomputer may execute all or part of the actual process to achieve theembodiments described above through the process.

Further, after the program code read from the recording medium iswritten into the function extendable board inserted into the computerand the memory provided in the function extendable unit connected to thecomputer, CPU provided in the function extendable board and functionextendable unit executes all or part of the actual process according tothe instruction of the program. The situation where the functions of theabove embodiments may be realized by means of the process is alsoincluded.

The present invention may have a plurality of varied embodiments withinthe spirit and scope of the invention. Therefore, it will be appreciatedthat, the scope of protection of the invention is defined by thefollowing claims, but not limited to the specific embodiments.

While the embodiments of the invention have been described in detailwith reference to attached drawings, various changes and modificationsmay be made to the above embodiments without departing from the spiritand scope of the invention. Therefore, the scope of the invention isonly defined by the attached claims.

The invention claimed is:
 1. A network system adopting a first IPprotocol, the network system comprising: an address allocating serverand a communication terminal supporting both the first IP protocol and asecond IP protocol different from the first IP protocol, the addressallocating server dynamically allocating an address of the second IPprotocol to the communication terminal, characterized in that: saidcommunication terminal comprises: a dynamic address manager foracquiring said dynamically allocated address of the second IP protocolof said communication terminal from the address allocating server suchthat the address of the second IP protocol is temporarily acquired andthen released after a specified time interval and acquiring a second IPprotocol address of a destination of a second IP protocol packet from asecond IP protocol application, and an address adapter for encapsulatingthe second IP protocol packet from the second IP protocol applicationinto a first IP protocol packet, wherein the second IP protocol addressof said communication terminal, included in a header of the second IPprotocol packet, and the second IP protocol address of the destinationare encapsulated into said first IP protocol packet; wherein saidaddress adapter further comprises: an address-mapping table for storinga correspondence between the first IP protocol address and the second IPprotocol address; an address-mapping table manager for managing theaddress-mapping table; a packet translator for transforming the first IPprotocol packet into the second IP protocol packet or transforming thesecond IP protocol packet into the first IP protocol packet, accordingto the correspondence stored in the address-mapping table; wherein saidfirst IP protocol packet is either an IPv4 packet or an IPv6 packet,said second IP protocol packet is an IPv6 packet when said first IPprotocol packet is an IPv4 packet and said second IP protocol packet isan IPv4 packet when said first IP protocol packet is an IPv6 packet. 2.The network system according to claim 1, characterized in that: saiddynamic address manager is operable to release said dynamicallyallocated second IP protocol address, in response to a notification ofthe ending of said second IP protocol application, and said addressallocating server is operable to mark said released second IP protocoladdress as available.
 3. The network system according to claim 1,characterized in that: idle fields in the IPv6 packet are deleted whileencapsulating the IPv6 packet into the IPv4 packet, and idle fields inthe IPv4 packet are deleted while encapsulating the IPv4 packet into theIPv6 packet.
 4. The network system according to claim 1 characterized inthat: when the communication terminal is a destination, the addressadapter transforms the received encapsulated first IP protocol packetinto the second IP protocol packet.
 5. A method of managing a networksystem adopting a first IP protocol, the network system comprising acommunication terminal supporting both the first IP protocol and asecond IP protocol different from the first IP protocol, the methodcomprising: in said communication terminal, acquiring a dynamicallyallocated address of the second IP protocol of said communicationterminal from an address allocating server such that the address of thesecond IP protocol is temporarily acquired and then released after aspecified time interval and acquiring a second IP protocol address of adestination of a second IP protocol packet from a second IP protocolapplication; in said communication terminal, encapsulating the second IPprotocol packet from the second IP protocol application into a first IPprotocol packet, wherein the second IP protocol address of saidcommunication terminal, included in the header of the second IP protocolpacket, and the second IP protocol address of the destination areencapsulated into said first IP protocol packet, and in saidcommunication terminal, sending out said first IP protocol packet;storing a correspondence between the first IP protocol address and thesecond IP protocol address in each communication terminal; transformingthe first IP protocol packet into the second IP protocol packet ortransforming the second IP protocol packet into the first IP protocolpacket, according to the correspondence stored in the address-mappingtable; wherein said first IP protocol packet is either an IPv4 packet oran IPv6 packet, said second IP protocol packet is an IPv6 packet whensaid first IP protocol packet is an IPv4 packet and said second IPprotocol packet is an IPv4 packet when said first IP protocol packet isan IPv6 packet.
 6. The method according to claim 5 further comprising:releasing said dynamically allocated second IP protocol address, inresponse to a notification of the ending of said second IP protocolapplication.
 7. The method according to claim 5 characterized in that:idle fields in the IPv6 packet are deleted while encapsulating the IPv6packet into the IPv4 packet, and idle fields in the IPv4 packet aredeleted while encapsulating the IPv4 packet into the IPv6 packet.
 8. Themethod according to claim 5 characterized in that: when thecommunication terminal is a destination, a received encapsulated firstIP protocol packet is transformed into the second IP protocol packet. 9.A communication terminal supporting both a first IP protocol and asecond IP protocol different from the first IP protocol, thecommunication terminal coupled to an address allocating server fordynamically allocating an address of the second IP protocol thereto,said communication terminal comprises: a dynamic address manager foracquiring said dynamically allocated address of the second IP protocolof said communication terminal from the address allocating server suchthat the address of the second IP protocol is temporarily acquired andthen released after a specified time interval and acquiring a second IPprotocol address of the destination of a second IP protocol packet froma second IP protocol application, an address adapter for encapsulatingthe second IP protocol packet from the second IP protocol applicationinto a first IP protocol packet, wherein the second IP protocol addressof said communication terminal, included in the header of the second IPprotocol packet, and the second IP protocol address of the destinationare encapsulated into said first IP protocol packet, and saidcommunication terminal is configured to send said first IP protocolpacket, an address-mapping table for storing a correspondence betweenthe first IP protocol address and the second IP protocol address; anaddress-mapping table manager for managing the address-mapping table,and a packet translator for transforming the first IP protocol packetinto the second IP protocol packet or transforming the second IPprotocol packet into the first IP protocol packet according to thecorrespondence stored in the address-mapping table; wherein said firstIP protocol packet is either an IPv4 packet or an IPv6 packet, saidsecond IP protocol packet is an IPv6 packet when said first IP protocolpacket is an IPv4 packet and said second IP protocol packet is an IPv4packet when said first IP protocol packet is an IPv6 packet.
 10. Thecommunication terminal according to claim 9, characterized in that: inresponse to a notification of the ending of said second IP protocolapplication, said dynamic address manager releases said dynamicallyallocated second IP protocol address and informs said address allocatingserver of the release.
 11. The communication terminal according to claim9, characterized in that: idle fields in the IPv6 packet are deletedwhile encapsulating the IPv6 packet into the IPv4 packet, and idlefields in the IPv4 packet are deleted while encapsulating the IPv4packet into the IPv6 packet.
 12. The communication terminal according toclaim 9, characterized in that: when the communication terminal is adestination, the address adapter transforms a received encapsulatedfirst IP protocol packet into the second IP protocol packet.
 13. Amethod of sending packets by a communication terminal supporting both afirst IP protocol and a second IP protocol different from the first IPprotocol, the communication terminal connected to an address allocatingserver for dynamically allocating an address of the second IP protocolthereto, the method comprising: acquiring a dynamically allocatedaddress of the second IP protocol of said communication terminal fromthe address allocating server such that the address of the second IPprotocol is temporarily acquired and then released after a specifiedtime interval and acquiring a second IP protocol address of thedestination of a second IP protocol packet from a second IP protocolapplication, and in said communication terminal, encapsulating thesecond IP protocol packet from the second IP protocol application into afirst IP protocol packet, wherein the second IP protocol address of saidcommunication terminal, included in the header of the second IP protocolpacket, and the second IP protocol address of the destination areencapsulated into said first IP protocol packet, and in saidcommunication terminal, sending said first IP protocol packet; storing acorrespondence between the first IP protocol address and the second IPprotocol address in each communication terminal; transforming the firstIP protocol packet into the second IP protocol packet or transformingthe second IP protocol packet into the first IP protocol packetaccording to the correspondence stored in the address-mapping table;wherein said first IP protocol packet is either an IPv4 packet or anIPv6 packet, said second IP protocol packet is an IPv6 packet when saidfirst IP protocol packet is an IPv4 packet and said second IP protocolpacket is an IPv4 packet when said first IP protocol packet is an IPv6packet.
 14. The method according to claim 13, characterized by:releasing said dynamically allocated second IP protocol address, inresponse to a notification of the ending of said second IP protocolapplication.
 15. The method according to claim 13, characterized inthat: idle fields in the IPv6 packet are deleted while encapsulating theIPv6 packet into the IPv4 packet, and idle fields in the IPv4 packet aredeleted while encapsulating the IPv4 packet into the IPv6 packet. 16.The method according to claim 13, characterized in that: when thecommunication terminal is a destination, a received encapsulated firstIP protocol packet is transformed into the second IP protocol packet.17. The network system according to claim 1, wherein said first protocolpacket includes a flag to identify whether the first protocol packet hasencapsulated the header of the second IP protocol packet.